1. Field of the Invention
The present invention regards a structure for electrically connecting a first body of semiconductor material overlaid by a second body of semiconductor material, a composite structure using the electric connection structure and a manufacturing process.
2. Description of the Related Art
In particular, the invention can be used for electrically connecting a first silicon wafer incorporating electronic components to a second silicon wafer incorporating a micromechanical structure and/or to the outside. The invention can likewise be used for electrically connecting the first wafer to a third body carried by the second wafer, as well as for connecting the first wafer to the outside when the first wafer is covered by a protection structure, and thus is not directly accessible. An example of a particular application is represented by a micro-electromechanical system including a first wafer incorporating a circuit for controlling the parameters defining the state of a micro-electromechanical structure (for example, the position of a microactuator); a second wafer incorporating the micro-electromechanical structure; and a third wafer forming a cap for protecting the micro-electromechanical structure.
Various techniques are known for mechanically connecting two semiconductor material bodies (see, for example, Martin A. Schmidt, xe2x80x9cWafer-to-Wafer Bonding for Microstructure Formationxe2x80x9d, Proceedings of the IEEE, Vol. 86, No. 8, August 1998). However, such techniques do not enable two or three wafers to be electrically connected, in addition to be mechanically connected, or covered components of one of the wafers to be electrically accessed.
An embodiment of the present invention provides a connection structure that enables semiconductor material bodies made on different substrates to be overlaid and to be connected mechanically and electrically together and to the outside.
According to embodiments of the present invention, an electric connection structure, a composite structure, and a process for manufacturing a composite structure are provided. The electric connection structure connects a first silicon body to conductive regions provided on the surface of a second silicon body arranged on the first body. The electric connection structure includes at least one plug region of silicon, which extends through the second body; at least one insulation region laterally surrounding the plug region; and at least one conductive electromechanical connection region arranged between the first body and the second body, and in electrical contact with the plug region and with conductive regions of the first body. To form the plug region, trenches are dug in a first wafer and are filled, at least partially, with insulating material. The plug region is fixed to a metal region provided on a second wafer, by performing a low-temperature heat treatment which causes a chemical reaction between the metal and the silicon. The first wafer is thinned until the trenches and electrical connections are formed on the free face of the first wafer.